For many surgical procedures, a patient is anesthetized and thereby rendered unconscious. In this condition, the patient is typically paralyzed and cannot breathe. Therefore, it is common to perform an endotracheal intubation whereby a tube, connected to an artificial breathing machine, is inserted into the patient's trachea. However, sometimes the anesthesiologist errs and inserts the tube into the esophagus. In the past, there was no way to know whether the tube was incorrectly inserted until the breathing machine was hooked up. Even then, it typically took several breaths and considerable expertise and expensive equipment to determine if the tube was in the esophagus. If it was, the intubation had to be attempted again. If the error was repeated a number of consecutive times, the patient could die.
A number of techniques have been developed to determine whether an intubation attempt is successful. For example, one currently employed technique uses capnography to measure intidal carbon dioxide levels. However, this equipment is very expensive and often requires several breaths before a stable reading is given. These are obviously undesirable drawbacks.